In a known shift range change apparatus of a vehicle, an electronic control device senses a shift range selected by a driver of the vehicle and controls a drive operation of a rotational drive apparatus according to a sensed value of the shift range to change a shift range of an automatic transmission with a torque outputted from the rotational drive apparatus.
For example, in the shift-by-wire system of JP2010-203543A, the rotational drive apparatus is connected to the shift range change apparatus of the automatic transmission and changes the shift range of the automatic transmission with a torque outputted from an output portion of the rotational drive apparatus. The rotational drive apparatus has a rotatable member, which is made of resin and has external teeth meshed with external teeth of the output portion. A magnet is installed to this rotatable member, and a magnetic flux generated from the magnet is sensed to sense a rotational position of the rotatable member. Thereby, a rotational position of the output portion and the shift position of the shift range change apparatus are indirectly sensed. Therefore, there is a possibility of deteriorating a sensing accuracy of a rotational position of the output portion due to, for example, backlash between the output portion and the rotatable member.
In the shift-by-wire system of JP2010-203543A, the output portion is made of a magnetic material, such as iron, to implement a sufficient strength. If the magnet is installed to the output portion to directly sense the rotational position of the output portion, the magnetic flux, which is generated from the magnet, flows into the output portion to possibly cause a reduction of the density of the magnetic flux to be sensed. In such a case, the sensing accuracy of the rotational position of the output portion may possibly be deteriorated.
In another rotational drive apparatus disclosed in JP5648564B2, an electric rotating machine and a speed reducing device are installed in a space located in an inside of a housing, which includes a front housing and a rear housing, such that the electric rotating machine is installed at the front housing side in the space, and the speed reducing device is installed at the rear housing side in the space. A speed of rotation (torque), which is outputted from the electric rotating machine, is reduced through the speed reducing device (serving as a gear mechanism), and the rotation (torque) of the reduced rotational speed is outputted to a manual shaft of a shift range change apparatus through an output portion. It is assumed that the rotational drive apparatus is installed such that the rear housing opposes or contacts an outer wall of the shift range change apparatus. The speed reducing device projects from a center of the electric rotating machine toward the shift range change apparatus. Therefore, a dead space, which is in a generally ring form, may possibly be formed between a portion of the outer wall of the rear housing, which is located around the speed reducing device, and the outer wall of the shift range change apparatus. Thus, installability of the rotational drive apparatus may possibly be deteriorated.
Furthermore, in the rotational drive apparatus of JP5648564B2, in a case where a magnetic flux density sensing device, which is provided to sense a rotational position of the output portion, is placed at the front housing side, the magnetic flux density sensing device is located adjacent to the electric rotating machine. Therefore, the sensing accuracy of the rotational position of the output portion may possibly be deteriorated by a leakage flux, which is a magnetic flux leaked from the electric rotating machine. In contrast, in a case where the magnetic flux density sensing device is installed at the rear housing side, which is far from the electric rotating machine, the dead space is further increased to possibly causing further deterioration of the installability of the rotational drive apparatus.